Rubber or rubberlike composition and method



Patented June 26, 1945 RUBBER OR RUBBERLIKE COMPOSITION AND METHOD Neil E. Tillotson, Watertown, Mass.

No Drawing.

12 Claims.

This invention relates to compositions of the type containing rubber or rubber-like materials and more particularly to compositions of said type containing a novel agent which provides for improved plasticity and tackiness of the compositions when employed as adhesives and during fabrication into articles to be vulcanized and an improved bond between plies of the rubber or rubber-like material or with other materials when vulcanizable compositions containing the agent are vulcanized, as well as rendering the unvulcanized rubber or rubber-like composition easier to mill and mix with various compounding ingredients. The invention also includes the method of improving the plasticity, tackiness and bond of compositions of the type above-mentioned.

The invention finds its major utility with rubber or rubber-like vulcanizable compositions which are deficient in the tackiness and plasticity which are necessary for successfully building up coherent multi-ply articles such as tires, for fabricating articles requiring joints or seams between various portions or for producing adherence between the vulcanizable composition and other materials. So-called synthetic rubber of the Buna S type which is a copolymer of butadiene and styrene polymerized in aqueous suspension, and certain types of reclaimed natural rubber are outstanding examples of materials of the rubber type which lack sufficient tackiness, bonding properties and plasticity for successful fabrication although many other rubber-like mate-" rials exhibit this deficiency to a greater or less degree. It has been proposed to add sufficient virgin natural rubber to such materials in order to impart the necessary plasticity, tackiness and bonding properties but the amount of such virgin rubber required is usually sufliciently great to defeat the very purpose of so-called synthetic rubbers or reclaimed rubbers, which is the production of compositions usable instead of virgin rubber.

In accordance with the present invention I have found that the resins or gums having the Application December 14, 1942, Serial No. 469,000

modulus of elasticity, elongation, tensile strength,

resistance to flex cracking, etc. While successful bonding is, in general, not obtainable in the absence of substantial tackiness of vulcanizable compositions prior to vulcanization, such tackiness does not insure the production of an effective bond or the preservation of the desired prop-' erties above enumerated, since tackiness itself may be produced by various materials which have no effect upon or even decrease the bonding characteristics upon vulcanization or destroy or impair certain or all of the desired properties above referred to. The increased bonding effect of the agent employed in the present invention may result at least in part from the fact that the agent is a viscous, sticky liquid or semi-liquid which is itself vulcanizable, i. e., it combines with sulphur or other known vulcanizing agents to form a more viscous semi-liquid,,plastic, or solid material which adheres tenaciously to other materials.

I have further found that with certain rubber or rubber-like materials the tackifiers or bonding agents of the present invention may be added in sufficient amounts to form a very substantial portion of the composition before deleteriously affecting the properties of the rubber or rubberlike materials so that the agents may be employed as extenders to reduce the amount of rubber or rubber-like materials necessary for the production of agiven article. In general the employment of substantial amounts of the bonding agents of the present invention also enable increased amounts of compounding ingredients or fillers such as carbon black, etc., to be employed without deleterious effect and in some casegeven with improved results to still further decrease the amount of rubber or rubber-like materials required. Also the addition of the agents of the present invention very materially increases the plasticity during milling of compositions containing rubber or rubber-like materials thus reducing the time and power required for milling of the composition and increasing the ease with which compounding ingredients may be added on the mill and the ease with which articles may be fabricated from the milled composition. It is therefore desirable to add the agent to the rubber or rubber-like materials early in the milling operation.

An object of the present invention is, therefore, to provide an improved composition containing rubber or rubber-like materials and a novel agent which improves the tackiness and plasticity of the composition.

Another object of the invention is to provide an improved rubber or rubber-like composition in which a vulcanizable bonding agent is employed to increase the plasticity and taejdness of a vulcanizable composition prior to vulcanization and to increase the bonding characteristics of the composition after vulcanization.

Another object of the invention is to provide an improved vulcanizable composition containing rubber or rubber-like materials deficient in tackiness and bonding properties, in which a natural vulcanizable gum or resin is added to obviate such deficiencies.

Another object of the invention is to provide an improved vulcanizable composition of the rubber or rubber-like type in which substantial amounts of a vulcanizable resin and increased amounts of other compounding ingredients are employed.

A further object of the invention is to provide a method of increasing the tackiness and plasticity of vulcanizable rubber or rubber-like composition normally deficient in such properties and increasing the bonding characteristics upon vulcanization of such composition.

A still further object of the invention is to provide an improved method of extending the rubber or rubber-like constituents without deleteriously ailecting the properties of such compositions.

The preferred bonding or extending agent of the present invention is the gum or resin obtained from the cativo tree (Prioria copaifera) which is a tropical tree of the Leguminosae family classified under the Caesalpiniaceae or Senna sub-family and the Cynometreae tribe. This tree is found in large numbers generally throughout Central America including Colombia and the Canal Zone. The gum or resin can be obtained from the tree by tapping and, as obtained from the tree is a viscous, sticky liquid'or semi-liquid of amber or brown color resembling honey in its physical characteristics and appears to be an oleo resin consisting essentially of resin acids of high molecular weight.

In addition to the stickiness of the resin which imparts tackiness to rubber or rubber-like compositions the more important properties of the resin are its capability of being vulcanized and its resistance to thermal decomposition and oxidation. The resin reacts with sulphur under suitable temperature conditions to produce more viscous sticky liquidsor plastics, or thermo-plastic solids depending upon the proportions of sulphur and conditions of vulcanization. A thermoplastic solid resembling gutta percha in its physical characteristics can be produced by employing sufiicient sulphur and the reaction responds to vulcanization accelerators in substantially the same manner as is the case in the vulcanization of rubber. Thus by employing known or suitable rubber vulcanization accelerators and terriperatures the rate and extent of vulcanization can be controlled in substantially any desired manner. Elevated temperatures with appropriate proportions of sulphur or accelerators or both can be employed to produce the desired vulcanization, either in conjunction with or in the absence of rubber or rubber-like vulcanizable materials. The vulcanized resin may thus be rendered more viscous or be converted into a plastic material while still retaining its tackiness and elasticity. By more drastic vulcanizing treatment, a hard thermoplastic solid having a relative high melting point can be produced which upon being softened or melted by the application of heat again becomes sticky or tacky. Excellent adherence of the hard solid to other materials can be obtained by vulcanizing the original resin to the hard state in contact with such other materials or cooling 9. heat softened or melted, previously vulcanized hard solid in contact with such other materials.

.cium oxide is somewhat slower.

The resin as it comes from the tree has relatively high boiling point, i. e. above 400 C., and can be boiled at atmospheric temperature without apparent thermal decomposition. It exhibits no evidence of thermal decomposition deleteriously affecting its properties at temperatures considerably above its boiling point. It has a somewhat disagreeable odor in its natural state but this odor is largely eliminated-upon heating to the boiling point and allowing a small amount of vapors to escape either at atmospheric pressure or at subatmospheric pressure, indicating the presence of a small amount of essential oils or highly volatile odoriferous material. This odor does not persist in vulcanized rubber or rubber-like products containing the resin. After escape of such volatile material the remaining material has a substantially constant boiling point and can be distilled either at atmospheric or subatmospheric pressure to leave a small amount of brown or darker residue indicating that the composition is probably essentially a single chemical compound. The distillate is a water white viscous, sticky liquid at atmospheric temperature similar except for color and odor to the original resin obtained from the tree. For most rubber compositions the resin obtained from the tree is suitable after straining to remove extraneou's material such as leaves, bark, etc., usually while heated, to reduce its viscosity. The distilled product, however, retains to a a large extent the properties of the crude resin discussed above and is particularly suitable for light colored or white vulcanized compositions.

An analysis of a typical sample of crude cativo The same resin when distilled to produce a water white distillate free from volatile ash, etc., gave an acid number of 177.1 and a saponiflcation number of 179.2.

The crude resin as well as the distilled resin is soluble in many organic solvents including hydrocarbon solvents. Thus one part of resin was found to be completely soluble in five parts of ethyl alcohol, butyl alcohol, ethyl acetate, toluene, petroleum ether, and carbontetrachloride.

The crude resin is incompletely soluble in acetone, the insoluble portion representing approximately 3% of the total resin.

The cativo resin either in the crude or distilled form, reacts readily with magnesium and calcium oxide to produce a hard brittle solid, but reacts with zinc oxide only at a greatly reduced rate. This latter material may. therefore, be employed as a compounding ingredient in vulcanizable compositions containing the resin in any suitable or usual proportions without deleterious effect upon the resin. The reaction with magnesium oxide takes place rapidly even at room temperature While the reaction with cal- The resulting products are thermo-plastic and when softened or melted by the applicationof heat become sticky or tacky in a manner similar to the vulplastic solids can be produced. Sulphur or other vulcanizing agents can be employed in varying proportions with the oxides to produce Products having various properties. In general the employment of sulphur or other vulcanization agents results in products resembling gutta percha whereas the employment of the oxides results in products having more rosin-like or more brittle physical properties. By varying the proportions of vulcanizing agent to oxides products can be obtained having properties intermediate between those above described. The resin can also be reacted with alkaline compounds of alkali metals. Thus sodium hydroxide may be employed to neutralize the acidity of the resin without much much change in the physical characteristics thereof. One effect is to somewhat increase the curing time and temperature during vulcanization.

The resin is particularly resistant to reaction with oxygen both in its free form and in combination with rubber or rubber-like material thus imparting anti-aging properties and even flame resistant properties to compositions in which it is employed in substantial amounts. Thus the flame resisting properties are retained when the resin is vulcanized or reacted with alkali metals or the various oxides discussed above, as well as when the resin is incorporated into rubber or rubber-like compositions. The resin itself or the reaction products discussed above'are not soluble in water but in most cases can be readily emulsified or suspended in finely divided form in water with suitable emulsifying agents. 4

When even small amounts, for example 1 to 2 percent by weight of the cativo resin on the basis of the rubber-like material employed, are incorporated into vulcanizable compositions containing synthetic rubbers which are deficient in tackiness, the plasticity and tackiness are increased sufliciently for most uses such as building up multi-ply articles or retreading tires and this adherence-persists in the vulcanized product causing the various layers to tenaciously cohere or adhere to other materials such as previously vulcanized rubber fabric, etc. It is rarely necessary to employ more than 2% of the resin and no case has been foundwhere more than 5% is required. Such small amounts of resin materially increase the workability of the composition and enable some increase in proportions of other compounding ingredients. The presence of the resin does not deleteriously affect the tensile strength, modulus of elasticity or elongation of the vulcanized composition and in some cases may even improve certain of these properties. In fact, with certain so-called synthetic rubber compositions, notably those containing Buna S, substantially no impairment ofthe desirable properties of the composition occur even when resin in amounts up to or or evendepending upon the character of the rubber or rubber-like materials, is incorporated into the composition. That is, the composition does not begin to assume resin-like characteristics until the resin content approaches 20 to 30% or the rubber or rubber-like constituents. For example with Buna S, 5 to 20% of the'resin may be advantageously employed as an extender al though 2 to 5% is usually suflicient for producing the required tackiness. The large amounts of resin have the further advantage of enabling greater amounts of other desirable compounding ingredients, such -as carbon black,-to be emwas approximately 57% of the total composition.

The carbon black selected was channel black a particularly hard" black, and with softer blacks even greater amounts can be employed. Furthermore, the composition containing the resin exhibited excellent tackiness and plasticity before vulcanizing and developed strong bonding properties upon vulcanizing, characteristics as to which Buna S is notably deficient. Also, the composition containing the resin required much less milling time and power to thoroughly plasticizethe same and incorporate the compounding ingredients.

Similar results can be obtained with compositions containing substantially any of the other synthetic rubbers. Thus, in many cases the resin can be employed in substantial amounts as an extender for natural or synthetic rubbers such as neoprene, which is polymerized chloroprene, a chlorine substituted butadiene, Buna N, which is a copolymer of butadiene and acrylic nitrile, 'I'hiocols which are olefin polysulfides, etc., irrespective of whether it. is necessary to increase the tackiness and bonding properties of the rubberlike materials. The amount of resin employed will depend upon the nature of the compounding ingredients used as well as that of the rubber or rubber-like materials and the characteristics of the article desired, so that no definite proportions can be given even for Buna S. In general, a small amount of resin, for example 2 to 5% is suflicient to supply a deficiency in plasticity, tackiness or bonding properties.

In some compositions amounts up to 15 to 25% or even 30% can be employed without substantially modifying the rubber-like .properties' of the compositions but greater amounts, for example 40 to 50% or more produce resin-like products which may, however, have some of the characteristics of rubber. In general, it has been found that smaller amounts, for example /2 to 5%, usually /2 to 2% of the resin must be employed with natural rubber compositions than with synthetics such as Buna S if the desirable rubber-like properties of the composition are retained. Thus with pure gum compositions, of the resin is usually sufficient while with natural rubber compositions which are heavily loaded with fillers and other compounding ingredients, up to 5% may be employed although 2% is usually sufficient. As a general rule, the greater the amount of resin which is employed within the limits above given, the greater the amount of other compounding ingredients on the basis of the rubber or rubber-like materials which can be incorporated into the vulcanizable composition without unduly increasing the hardness of the vulcanized product. The resin may thus tensile strength, elongation, modulus oi elasticity. etc. With certain rubber-like materials, notably Runs. 8, certain of these properties are materially improved. It will be apparent that the amounts and nature of the other compounding ingredients will vary as in the usual rubber technology depending upon the characteristics desired in the final product.

Vulcanization of rubber or rubber-like compositions containing the resin of the present invention is in general similar to vulcanization of the various compositions not containing the resin. Sumcient sulphur either as iree sulphur or in compounds such as certain accelerators containing available sulphur or equivalent vulcanizing materials known to the art must be supplied in Tut: I

Composition 1 2 3 4 100 100 l l 3 3 1. 5 l. 5 5. 6 2 2 150 150 Tum: III

Tensile properties 5 'r 1; s 'r a s '1 11 s 'r 11 510040400110 $401,010 1120 300510110 140110 07011034112701.210 s20 momooasoaaommm 575 700 3116 2801,210 610 0001,120 s30 3101.110 010 Tear resistance 15 min 130 120 49 30 min 105 105 160 45 min 105 180 110 Share hardness 30 min 59 52 61 51 Tun: IV

Composition 13 14 i5 BunaS 10c 100 100 Agerite white l l i a a a s0 00 so 1. 1. 1. 2' 2' 2' Tear resistance 15 min 140 210 30 min l 120 220 45 min 115 180 180 Shore hardness 30 min 83 50 .81

TAILI II Composition 7 8 Buna s...- 100 100 100 100 Aaerite white l l l l Zinc oxide 3 3 3 3 Alta: 1.: 1.: 1.: 1.: ifir i 'I 2' 2' 2' 2' P4: 100 100 100 1110 Cativoresin 2o 30 4 so Tensile Properties w s'rss'rns'rns'rn 15min 1,2ao1,assmm1,1m14s asouaouorostasm 30min 1,2st1,2z0a10o1o1,a10so0 4ao1,sssa1os4o1,nos1o 45min 1,24o1,ao5s15m1,7sa04owotaaomsssuoom Tear resistance 15 min 220 30 min 210 155 180 45 min 160 I 200 210 60 min 200 Shore hardness 30 min 88 59 55 Tm: V

Composition l6 l7 i8 1.0 1.: m .5 s Cativo resin a0 Gum thus (crude turpentine) so Tensile properties 3 which contains approximately 35% Buna S has substantially the same physical properties as E s T E S T E composition 1 which contains approximately 48% Buna S. Composition 4 which differs from com- 5 position 3 by the addition of more cativo resin is a s 8 T 1150 1,465 405 575 1845 760 230 410 920 11195 1,395 390 655 1:810 7m 320 600 880 still a good product in comparison with compo- 1,240 1,395 360 680 1,690 e65 350 690 770 tion 1 although t contains even less Buna S.

Referring to the examples of Table II, which Tesistmce difler essentially from the examples of Table I 10 by the employment of a different carbon black,

g3 it will be noted that equivalent compositions pro 45 mm 150 220 130 duce about the same result with either Thermax carbon black or P-33 carbon black, the only ma- Shore hardness 3'01 diigerence being that the P-33 carbon black main ins the hardness more near the sam as 30 mm 65 55 72 cativo resin i added. e

In the above tables under Tensile properties, The compositions of Table III in comparison S refers to the stress in pounds per square inch with the compositions of Tables I and 11 show of the original cross-section at 300% elongation that soft carbon black are much mor effective usually referred to in the rubber art as the in developing high tensile strengths and other modulus of elasticity; T refers to the tensile desirable properties with synthetic rubber comstress at rupture in pounds per square inch of positions than is the case with clays. It will be the original cross-section; and "E refers to the noted that the presence of small amounts of percent elongation at rupture of specimens subcativo resin very materially increase the tensile jected to test in a standard testing machine. The strength and the elongation of compositions contear resistance is given in pounds per tenth of taining Kalvan clay, but was not as effective with an inch thickness as the stress necessary to tear Dixie clay. a crescent shaped specimen providing differential Referring to Table IV it will be noted by comtension between the two curved edges in accordparison of compositions 13 and 14, that the addiance with the standard Goodrich method while tion of 20% cativo resin left the tensile strength the hardness was determined with the Shore of compositions containing a hard carbon black durometen approximately the same while decreasing the In the various compositions above given, Agermodulusand increasing the elongation. Thetear ite White is N,N'di-beta-naphthyl-para-phenylresistance remained substantially the-same while enediamine (an age resistor); Altax is benzolthe hardness was somewhat decreased. Composithiozyl disulphide (an accelerator) D. P. G. is tion 15 in comparison with composition 14 shows diphenylguanidine (an accelerator); Thermax is hat pine tar, a common plasticizer in rubber a soft carbon black; P-33 is another soft carbon compositions, is not the equivalent of cativo resin black; Kalvan is a clay employed in many rubas this material very much lowered the tensile ber compositions. and the same is true of Dixie 40 s rength and hardness although the elon n clay; channel black is a hard carbon black and was increased and the modulus lowered.

gum thus is a crude, almost solid, turpentine. Referring to Table V, compositions 16 and 17 While for the purpose of providing comparative therein contain the same materials in the same tests, Buna s has been employed as the rubberpr p ti ns as ompositions 5 and 6, respe v like material throughout the above examples, it 4 of Table II, but were made and vulcanized on a is to be understood that similar results can be difierent date. The properties of the equivalent obtained with other synthetic rubbers. compositions agree very closely, but due to un- Referring to Table I, it will be noted that the avoidable slight differences in procedure, particucomposition 2 which differs from composition 1 larly in vulcanizing conditions, are not identical. solely by the addition of 20% cativo resin de- Table 15 given to Co pare the effect of cativo veloped a much higher tensile strength after vulresin and gum thus upon the p y i l P p r canization as well as a much lower modulus and 01 1311119- c p t n p t nS 16 a d l a much higher elongation. The tear resistance uplicate comp sitions 5 and 6 of Table II in was also substantially doubled although the hard- Order to Provide a comparison With composition ness was considerably decreased. In interpreting 66 18 whloh was processed under the a e co the figures under the heading Tensile properties tions as compositions 16 and 1,7- It W111 be noted in all of the tables, the greatest figure in any that t e d ti n of 0% catlvo resin to composicolumn is usually given the greatest weight as t"i011 16 to Produce p on 17, v y materially even Slight changes in composition 111 frequently increases the tensile strength, decreases the modvary the curing time f r optimum properties and go ulus and increases the elongation and resistance in commercial operations the curing time which to tear, Whlle decreosmg the hardness- 011 the dev lo th desired ro erties is selected. The other hand, gum us creased the ns 51 51 tear E strength to about half that of compos1t1on 16, al-

om osltions 1, 2, and 3, the though it decreased the modulus and increased laa g ggrm g g 13 composition 2 only by as the elongation, but also materially decreased the a. incl-ease of carbon black, shows that tear resistance while at the same time very much creasing the carbon black somewhat reduces the mcleasmg e hardnesstensile strength and increases the hardness while Fmmthe ve examples it will be seen that t t same t increasing t modulus and the addition of substantial amounts of cativo ressomewhat decreasing the elongation. In fact a 70 m t onal vulcanizable rubber-like comcomparison of compositions 1 and 3 will show that positions containing Buna S in generalimproves the physical properties are or substantially the the desirable quahtles of s h p sm ns, parsame order in both of these compositions, alticularhl those f n g f carbon black. In though composition 3 contains 50% more carbon any event there is, 111 general. h Imp irment of black and 20% cativo resin. Thus. composition .75 e d sirable qualiti s- AlSO, in ner l, addithe vulcanized composition are at the same time increased.

It will also be apparent that the resin of the present invention is an advantageous ingredient of rubber adhesives. Such adhesives are generally unvulcanized compositions containing rubber or rubber-like materials and desirably have a permanent tack. The resin increases the tackiness of such adhesives and because of its high stability, i. e. resistance to oxidation, drying, etc., the adhesives do not lose their desirable properties over long periods of time. It forms an effective adhesive ingredient in such products as rubber tape for electrical insulation or in friction tapes. Also, adhesives may either by employed as a solution in rubber solvents or as an aqueous suspension, for example in rubber cements or shoe cements. The resin is not soluble in water but may be easily emulsified in water by substantially any of the known emulsifying agents tending to produce oil in water emulsions. Thus the resin may be incorporated into natural or artificial latex cements.

:properties which are retained when admixed with rubber or rubber-like compositions. By the term rubber or rubber-like materials" as employed herein is meant polymers of the elastomer type including natural rubber and so-called synthetic rubber such as Buna S, Buna N, Thiocols, neo-' prene, etc., which resemble natural rubber as to physical properties.

While I have disclosed the preferred embodiment of my invention, it is understood that the details thereof may be varied within the scope of the following claims.

I claim:

1. A composition of matter comprising a butadiene rubber material in which is incorporated a sticky, substantially non-oxidizable, iiame resistant vegetable resin selected from the group consisting of cativo resin and copaiba resin.

2. A composition of matter having adhesive properties comprising a butadiene rubber containing a substantial amount of an added resin selected from the group consisting of cativo resin and copaiba resin, said resin being present in h an amount materially less than the amount of While cativo resin has been specifically discussed above, resins from other related trees or plants may also be employed. It has been found I that the resin from the copaiba tree (C' paifera oflicinalis) also sometimes known as the copaiva tree is essentially similar to the resin from the cativo tree except that it usually contains a greater amount of volatile material or essential oils whicncan be removed by heating. This tree is found throughout tropical America and is classified in the same sub-family and tribe as the cativo tree. There are a large number of species of trees classified under the genus copaifera, many of which also yield resins having the characteristics of the cativo resin although the cativo tree is placed under a different genus, namely Prior-ta, and represents the only known species under. that .genus. It can, therefore, be reasonably predicted that many other trees or'shrubs classified under the tribe Cynometreae will also yield resins having the characteristics of cativo resins and that the same is true of trees or shrubs classified under the sub-family Caesalpinioideaev The botanical classification for this sub-family is as follows:

The present invention is therefore concerned with the employment of resins having the charthe butadiene rubber.

3. A vulcanizabie composition comprising a butadiene rubber deficient in tackiness and bonding properties and a viscous, sticky vulcanizable substantially non-oxidizable vegetable resin selected from the group consisting of cativo resin and copaiba resin and added in sufilcient amount to render said composition tacky and impart improved bonding properties to said composition when vulcanized.

4. A composition of matter capable of being vulcanized to produce a product having rubberlike properties, said composition comprising a vulcanizable butadiene rubber, a vuicanizing agent, a substantial amount of an added viscous, sticky, substantially non-oxidi'zable, vulcanizable vegetable resin selected from the group consisting of cativo resin and copaiba resin, and other rubvulcanizable butadiene rubber material, a vuland bonding properties, a substantial p p rtionof carbon black, and a viscous, sticky vulcanizable resin selected from the group consisting of cativo resin and copaiba resin in suilicient amoimt.

to render said composition tacky and impart improved bonding properties to said composition whenvulcanized,saidresinbeingaddedin amounts between 20 and 30% of the rubber or acteristics of the resin from the cativo tree. WA- 76 er-like material and being characterised by izable vegetable resin selected from the group I consisting of cativo resin and copaiba resin in an amount between and of the butadiene rubber, and suillcient carbon black to provide the I composition with the desired hardness without substantial impairment of the elasticity and tensile strength of the composition when vulcanized.

8. A vulcanizable composition comprising a butadiene rubber deficient in tackiness and bonding properties admixed with a viscous, stticky, vulcanizable substantially non-oxidizable vegetable resin selected from the group consisting of cativo resin and copaiba resin in amounts between approximately 1 and 5% by weight of said butadiene rubber.

9. A vulcanizable composition comprising a vulcanizable butadiene rubber deficient in tackiness and bonding properties admixed with a viscous, sticky, vulcanizable substantially non-oxidizable vegetable resin selected from the group consisting of cativo resin and copaiba resin in amounts between approximately 1 and by weight of said butadiene rubber.

10. .A vulcanizable composition comprising a vulcanizable butadiene rubber mixed with approximately 1 to 30% of cativo resin by weight on the basis of the amount of said butadiene rubber in said composition.

11. A vulcanizable composition comprising a vulcanizable butadiene rubber, rubber compounding ingredients and an amount of cativo resin between approximately 1 and 30% by weight on the basis of the amount of said butadiene rubber in said composition. a

12. A composition of matter comprising a butadiene rubber, rubber compounding ingredients, and a substantial amount of an added resin selected from the group consisting of cativo resin and copaiba resin, said resin being present in an amount materially less than the amount of butadiene rubber.

NEIL E. TILLOTSON. 

